Electric phonograph reproducer



A. A. THOMAS ELECTRIC 4PHONOGRAM REPRODUCER Sept. 7 l1926.

Waltentetl Sept# 7, 1926.

unirsi)v STATES .ADOLPH A. THOMAS, 0F NEW YORK, Il. Y.

ELECTRC PQNOGRAPH REPBODUOER.

- Application filed December 30, 1925. Serial No. 78,277.

Thi@l invention relates to devices for elec* tricairv reproducing`sound, and its object is to provide new and improved electromagneticreproducing mechanism controlled by l! a needle or stylus arranged to bemechanieab' ly actuated by a medium of recorded sound, such as aphonograph record and the like. My new instrument is characterized bythe absence of a diaphragm, by a vibratorv unit ot" such low inertia`and high elliciency as'to reproduce the most delicately recorded sound,and buv a construction otA utmost simplicity.

In phonograph records heretofore made, the spiral track usually hasabout 80-lOO lines to the inch, and a l2-inch record plays about veminutes. By mans of improved recording methods it has been proposed tomake records with several hundred lines to the inch, so that. a. singlerecord will pla'v lo'r halt an hour and longer. Now. with such 'linelyvcut record grooves, the use of a mechanical reproduee'r is out of thequestion. The high-inertia of the stiff diaphragm would be too muchforlhe delicate vibrations ot' the needle and would be liable to'brcakdown the Vfrail walls of adjacent ls'ooves The same objection applies toa reproducer oi' the microphone type. where ay diaphragm`opcratesagainst packed resist,- ance granules.

ln the electric reprodnccr of niv-'invenlion. the vibrator?,Y unitactuated by ,the needle is so light as to have no appreciable inetia.and its vilnations are. not dampened or impeded bvanv magnetic drag;Y4ot the electroniagnetic mechanism. As a result. the vibratory unitresponds freel)vv and l'ail'h-' full)P lo the minutcst vibrationsproduced ou the needle by the record groove. To this cud. I mount on thelfree end ot' the needle arm a lfrcely movable coil arranged to vibratein a magnetic ail-gap to cut the lilies ol lorcc. The vibrations ot thecoil thus gcn- 5 crate an electriccurrent. which is amplilicd h v any.suitable means to operaie a loudspeaker or other telephone receivingdevice. The mounting` ot the coil is such that the vibrations at theneedle point are transiniltmlto the coil inv greatly: amplilied ratio.so that the smallest movement otl the needle produces `s'uliicicntmovement ot' the coil to generate a currentin its circuit. The entiremechanism is exceedingly simple and may be housed in a little casingproperly .exaggerated scale, taken mounted to allow the needle to travelover the record.

` In order to explain my invention so that those skilled .in the art mayunderstand and use the same, I have selected two illustrativeembodiments as shown in the accompanying drawings, which I shall nowdescribe in detail. In these drawings- Fig. l is a tace view of anelectric reproducer coing-'tructed in accordance wit-h my invention, thecover ot the casing being removed to show the interior;

Fig. 2 is a cross-section approximately on the broken line 2-2 of Fig.l;

il is a plan 'iew in section on line 3--3 ot Fig. l, showing` thearrangement of springs tor norn'ialljiv centralizing the needle arm gFig. 4 is a detached sectional view larlcd scale to show on an en themounting' of the vibratory coil on the tree end of the needle arm;

Fie'. represents diagraminaticallythe various positions ot the coil withrespect to the pole pieces of the magnet;

Fig. 6 shows an interior face view ofa modified forni ot reproducercmbodving mv invention: i u

Fig'. T a cross-sectional View approximatchv on the broken line 7-7 ofFig. G;

i Figi. S is a fragmentary view, on a greatly approximatel;Y on thebroken line 8--8 ot Fig i' to show the construction of the front spring'for the needle arm; and

hier. S). is an enlarged Jtragmentar)7 view on line UMS) ol Fig. 7,showingr the rear spring t'or the needle arnn llclore taking' up thesedrawings in detail. Ict me explain that the partsare purposely shown inexaggerated din'iensions, So as lo make the figures as clear aspossible.

.'lhe actual constructionofv the reproducer is considerably more thedrawings.

Referring lirst to the embodiment trated in Figs. l-l. there is a suitacompact` than shown in illus ble casing .indicated as a whole by C forhousing the dill'erent parts ol the reproducer. The casinfr C is hereshown circular in form, consisting olf a back plate l. a cylindricalbod)T section 2 and a removable front plate I. The back plate l isprovided with a hub 4;, by .means ot' which the reproducer is removablymounted on a suitable supporting arm 5, which .allows the instrument totravel' over a record. The casing C is preferably' formed of thin lightmetal, such as alunnnuin, or an aluminum alloy, which is suiticientlyrigid and is nn-magnet1clfwde,- sired, however, the casing may beshaped. or molded out of suitable insulating'material, such as bakeliteor other compositie-n hetY- ing the requisite stren h.

A needle arm 6 is pivoted to casing C in any suitable Way. In thepresent instance, l have shown the casing provided Withl e pair of lugs7,.in which are mounted ad]ust able bearing screws 8 having pointed endsfor pivotally supporting the needle arm. The outer end of needle arm 6is in the orm o a needle holder 9. In the broader aspect of myinvention, the needle holder need n ot be a direct or integral part ofthe needle arm, for these two parts may be separately mounted andproperly connected for simultaneous operation.

Nithin the casing C is mounted a erniaA nent magnet indicated as a Wholey ld. For convenience I have shown the magnet mounted on the back wallof the casing an secured in pbsition by screws l() or otherwise. Themagnet M is preferably circular, 'following closely the outline of thecylindrical body section 2 of the casing, whereby a magnet oi' maximumlength is obtained. The magnet terminates in a pair ot projections ll,extending forwardly ot' the casino'. These projections may be formedintegral with the body of the magnet. To the pro jections'll. aresecured pole pieces 12 of soit iron7 or of any suitable alloy havinghigh magnetic permeability. The pole pieces 12, which are cylindrical inthis case, are arranged in axial alignment to provide an eirgap 1?, inwhich vibrates a coil 14 suitably mounted on the inner end of the needlearm 6. In the drawings I have shown the needle erm terminating in arearwardly projecting lug l5, to which is clamped a band 16 by means ofa screw or rivet 1T. he band i6, which may simply be a strip of anysuitable xnateriah' tightly surrounds the coil il and holds the semerigidly attached to the needle arm. The ends 18 ot the coil areconnected to a pair ot binding posts 1E) mounted on the rear Wall l otthe casing. Conductors 20 lead from the binding posts 1S to suitableapparatus for amplifying the currents generated in coil le duringtheyvibrations of the needle arin G. 'lt the supporting arin 5 Jfor thereproduccr is e hollow tube, as shown in Fig. 2, the connecting wiresPlvmaybe housed invisibly in this tube. thereby adding to the neatnessoit the machine in which the reproducer is mounted.

Suitable spring means is provided to hold the needle arm S normally inpredetermined position. In Fig. 2, I have shown a pair of springpressedtballs 2i arranged to engage Lseeeee the needle arm on opposite sides inthe piane of its vibret-ifins. 'lfhe bells 2l ere mounted in smallcylindrical housings 22 and 23, and are pushed against the needle erm bycoil springs 24. The normal tension ot these 'springs is adjustable bymeans oi screws The back Wall et the casing may be provided with a hole26 in alignment with screw25, so as to permit the insertion of aninstrument for adjusting the screw. The iront spring housing 22 iscarried by (or forms part of) ay bracket 2T, asbest shown in Fig. 3.rlhe bracket 27 is secured by screws 25 to a pair of lugs 29 proiectingupwardly Irom the bottoni or the casing. The lugs 29 are connected atthe upper end by a crosspiece 30, which carries the rear spring housing23, it will be understood that the spring housings 22 and aresuflicientiy spaced at their inner` ends to allow for the maximumvibrations of the needle arm at that point "lhe springs are adjusted togive the coil a normal posi-tion with respect to the magnetic polepieces 12. In Fig. 2, the normal position of the needle erm G is suchthat the axis of the cylindrical coil 14 is substantially coincidentwith the axis oit the cylindrical pole pieces. l`his means that normallythe maximum magnetic flux passes through the coil l2. During thevibrations of the needle arm 6. by means of a needle playing a record,the number of magnetic lines ot torce passing through 'coil lll variedin. accordance with the amplitude of vibrations of the needle arm. Thevariable currents thus generated in thecoil lfl are passed through asuitable amplifying device which .operates or controls a telephonereceiver acoustieaily connected with a horn or other soundmmpliiyingdevice.

it. will be clear trom Fig. 2 that the vi brations at the needle kpointare consider- `ably amplified in being transmitted to thelcurient-generatin,ey coil lll. Consequently, the miuutest vibrations etthe needle pro-- duce sutlicient movement of coil lll te qeuerate anelectric current of variable impulsesA llhile these impulses are veryWeek, there is no dilliculty in properly amplifying them forloudspeaking repreduction.v .eis these aluplityincr arrangements areWell understood by those skilled in the art, i need not show or describethem, particularly since myyinvention has nothing to do with suchaccessories. f

The normal position ot coil 14C with respect to the magnetic poles l2,or the airgap 13, may be other than that shown in Fig. 2. For example.in Fig. 5 the dotted circle lila represents the normal position -o thecoil 14;, and the dotted circle 14 is intended to indicate roughly theextreme position of thev coil i4 to one side ot its normal Y' or centralposition. The other extreme po,-

Cil

sition of the coil may be considered to be the same as the 12 in Fig. 5.When the coil moves toward the pole pieces. the magnetic flux passingthrough the coil is increased. Conversely, when the coil moves out otthe airgap toward the position 14.", the magnetic flux passing `throughthe coil is decreased. It will, 'of course, be understood that thevarious positions ot' the coil 14 in Fig. 5 are indicated merely in adiagrammatic way, and are considerably exaggerated. In actual practice,the maximum amplitude ot' vibration of coil 14 will be very small.

The coil 1ct may be made exceedingly light, so as to add very littleweight and resistance to .the needle arm (3. To that end, the coil ispreferably wound on a cylindrical core 3l of very light 1miterial,`suchas bakelite and the like. The shell 31 had better be/made ofnon-metallic material, so as to avcfid induced currents therein whichmight have a disturbing effect.

The needle arm G with its needle holder 9 can be made ot' light, strongmaterial. such as aluminum, so that the inertia ot the vibratory arm andcoil ll may be reduced to a practical minimum. The springs 24 should bejust strong enough to'hold the needle arm and coillelV in normalposition and to offer the, proper amount of resistance to the vibrationsproduced by the needle. This produces a vibratoi'y unit which as a.whole possesses minimum inertia and correctly responds to the mostdelicate Vibrations of the needle. Consequently, my new instrument ismirticularly adapted tor play` ing records in which the spiral trackconsists oi" many more lines to the inch than in previous phonographrecords that were inechanically reproduced by diaphragms.

ln the excmplification shown in Figs. 6,-8, there is a casing'substantially rectangular in shape, Otherwise,- what has been said aboutthe construction and iiounting of casmay be considered applicable tocasingv ingr L C. A needle arm 32 is pivoted to casing by means of'adjustable bearings '33, or in any other practical way. A magnet M isfirmly mounted within ,the casing, 'as by means ot' screws 34 whiclisecure the magnet against the back wall of the casing. As

sho-wn in Fig. 6, the magnet is substantially rectangular and closelyfollows the outline ot' the casingfso as to provide a magnetic path ot'maximum length in a small space'. Since the body of the magnet is flat,it may be .stamped out of magnet steel, either solid or laminated. rlhemagnet M compris i a pair ot outer limbs 35 and-a middle limb The outerlimbs 35 are of the same polarity and by a magnetic cross-piece 3 areconnected which is shaped at the center into a ring 38. llhe cross-piece37 is made of soft ironland is rigidly connected to the limbs 35 bysuitposition of the pole pieceI paper, liber,

: ing

polar ring 38. The pole piece Ll() is cylindrical in shape and isarranged coaxially with the ring 38, so as to provide an annular air-.gap tot substantially uniform width. As shown in Fig. 7, the polar ring38, which may be considered as one of the magnetic pole pieces, isoffset with respect to the Hat body of the magnet, so as to preventshortcircuiting of the flux across the central limb 36. Since the ,parts38 and Ll() constitute the two pole pieces of the magnet, the flux willytraverse the annular airgap L11 all around.

To the tree or inner end of the needle arm -32 is attached a cylindricalcoil 42, which is arranged coaxially in the airgap 41, so as to vibratetherein. In the present instance the coil 12 is shown mounted on a cup43 of light.

thin material, preferably non-metallic, such as balrelitc. tiber, stillpaper and the like. The cup 13 is fastened to the needle arm 32 by meansot' one or more lugs 44 struck up at thc inner end of the needle arm soas to lie flat against the end of the cup. The front vall of cup 13 ispreferably in skeleton form, or may be provided with air holes 115, soas to prevent. (he forming of air cushions during the vibrations of thecoil. Any other practical means may be used for securely attaching thecoil 42 to the free end ot the needle arm.

Suitable spring means is employed to hold the curient-generating coil 42in normal position in the annular nii-gap 4l, as indicated in Fig.y T.,ln the present inodilication l have shown a pair of springs t6 and t?arranged in the casing so as to engage the needle. arm 32 at oppositesides in the plane of its vibration. The front spring 4G is' mounted ona pair oic lugs 48 to which it is secured by screws 4S), as shown inFig. 8. A set-screw 5i) adjusts the normal pressure of spring 4G againstthc needle arm. The adjusting screw 5() is mounted in a plate 5l, whichis secured -to thelugs 48 by the screws 49. As shown in Fig. 8. thespring 46 is formed at its lower end with integral side flanges itl audthese flanges are held rigidly clamped between the supi'iortinjr lugs 4Sand the plate 5l. The rear spring 4i is mounted on a lug 52, which maybe struck up from thebody ot the'casing, thereby providing at thesametime a slot ethrough which the needle arm 32 extends into the casing.The spring 47 is secured at its lower end to the lug 52 by screws aretaining plate rl`he plate 55 carries a screw 56 for adjusting Ithenormal tension oi spring 4t?. It goes without saying that the rearspring et? is adjusted bet'ore the central section ofthe casis connectedto the rear wall thereof.

55 being interposed.`

` axial alignment with sai Orr the'baek wall of casing C are mountedinsulated binding Vposts 57, to which are connected the leading-outwires 58 ot the coil 4Q. Conductors 59 lead from the hinding posts 57 tosuitable circuit connections for including the coil' 42 operatively incircuit. Whathas been previously said concerning the operation of coil14: andthe amplification of the currents generated thereby, is fullyapplicable to coil 42 Without repetition.

Although I have shovvn and described two specific constructions otmyinvention, I want it understood that I. have done so merely by way ofexample and not as a restriction or limitation. It is evident that thebasic ieaturcs of my invention can be mechanically embodied in variousother moditications. n

vWhen I refer to my invention as a phonograph reproducer, I use the Wordphond graph in its broadest possible sense of recorded sound. Theparticular type or name of soundreproducing machine in which myinvention is embodied, is imma` terial.

llVhat I claim as my invention is:

l. ln an electric phonograph reproducer,

a vibratory lever` pivotally mounted so as to be actuated by thevibrations of a record needle and having a free inner end, a magnethaving an airgap, and a coil mounted on the free end of said lever so asto vibrate insaid airgap to cut the magnetic iiux.

2. An electric phonograph reproducer having a magnet, and a vibratoryneedle arm pivotally. mounted and carrying at its free end acurrent-generating coil arranged to vibrate relatively to said magnet inamplified ratio to the needle vibrations.

3. In an electric sound reproducer, a magnet having an airgap, avibratory lever pivoted near one end thereoso as to provide a shortarmand a iong arm` acoustic means 'for mechanically vibrating the shortarm, and a freely movable coil mounted on the free end oi said long armand arranged to vibrate in said 'airgap to cut the magnetic linx.

Al. In an electric sound reproducer, a cas ing, a magnet mounted in saidcasing and provided with a pair of pole pieces arranged in axialalignment to provide an airgap, a. vibratory lever pivotedj near one endthereof sq as to provide a short arm and along arm, said lever beingmounted to vibrate transversely of Said casing, acoustic means formechanically vibrating the short arm, a coil mounted on the free end ofsaid long arm in a position to vibrate across said airgap transverselyof said casing, and nonacoustic resilient means for normally holdingsaid coil in said airga in substantially pole pieces.

5. An electric phonograph reproducer comprising a casing, a needle armpivot-ed to the lower portion of said casing, the pivot point of saidarm dividing the sameinto a short `outer section and a long innersection, a magnet mounted in said casing and having an airgap near'theupper end of the casing, a coil mounted on the free end of said longsection of the needle arm and arranged to; vibrate in said airgap inamplified ratio to' the needle vibrations, and non-acoustic resilientmeans for normally holding said needle arm and said coil inpredetermined:

position.

6. I n an electric phonograph reproducer, a casing provided at-its lowerend with a pivoted needle holder, a vibratory arm arranged Within saidcasing and connected at one .end to said needle holder, a magnet somounted in said casing that the magnetic airgap is near the upper end ofthe casing diametrically opposite said needle holder, and a coil carriedby the free end of'said arm and arranged to vibrate in said airgaptrans' versely of the casing to out the magnetic airgap to cut themagnetic ilux, so that variable currents are generated inthe circuit osaid coll in accordancewith the vlbrations of the needle 1n said holder.the arms of said lever being so proportioned in length that the needlevibrations are transmitted to the coil in amplified ratio, andnon-aconsl tic resilient means for normally holdingsaifl said polepieces.

8. In an electric sound reproduc'er, a mag net provided with pole piecesarranged tol form an annular ai'rgap, a vibratory lever pivoted near oneend thereof sol as to provide a,y short arm and .a .long arm, acousticmeans for mechanically vibrating the short arm, and a cylindrical coilmounted on said long arm so as Ato vibrate axiallir in said annularairgap.

.9. An electric phonograph reproduccicomprising a. shallow casinghavlng' substantially parallel'front and rear Walls, a.

magnet mounted 'atwise in said casing against one of said walls andhaving .pole

piecesarranged to provide an airgap near'' the upper, portion of said.casing,l a needle arm pivoted near one end to the lower por- .coil inpredetermined position relative to l iso tion of said casingdiametrically opposite saidairgap, the longer' section of said armextendingtoward th magnetic pole pieces, a coil mounted on the freeinner end of said arm to vibrate across said ail-gap, and adjustablemeans for normally holding said coil in predetermined relation to saidairgap.

10. In an electric phonograph reproducer having a casing, a'leverpivoted to said casing andadapted to beactuated by a record needle, apair of springpressed members mounted in said, casing and arranged tobear yieldingly against opposite sides of said lever for normallyholding the same in predeterminedposition, said members having roundedsurfaces in Contact with said lever, and electromagnetic mechanismoperated by said lever.

11. In an electric phonographleproducer having a casing, a pivotedle'ver adapted to be actuated by the vibrations-of a; record needle,electric reproducing mechanism Within said casing' operated by saidlever, Vand a pair of spring-pressed members arranged within said casingto engage said lever at opposite sides inthe plane of its vibrations fornormally holding the lever in predetermined position.

12. 'In an electric phonograph reproducer, a pivoted lever adapted to beactuated by thc vibrations of a record needle, electric reproducingmechanism operated by said le'- ver, a pair of spring-pressed ballsarranged to engage said lever at opposite sides in the'. lplane of itsvibrations for normally holdin the lever in predetermined position, anmeans to adjust the normal `ball "against said lever.

ADOLPH A. THOMAS.

pressure of each

